nir_repair_ssa.c revision 7e102996 
1/*
2 * Copyright © 2016 Intel Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 */
23
24#include "nir.h"
25#include "nir_phi_builder.h"
26
27struct repair_ssa_state {
28   nir_function_impl *impl;
29
30   BITSET_WORD *def_set;
31   struct nir_phi_builder *phi_builder;
32
33   bool progress;
34};
35
36/* Get ready to build a phi and return the builder */
37static struct nir_phi_builder *
38prep_build_phi(struct repair_ssa_state *state)
39{
40   const unsigned num_words = BITSET_WORDS(state->impl->num_blocks);
41
42   /* We create the phi builder on-demand. */
43   if (state->phi_builder == NULL) {
44      state->phi_builder = nir_phi_builder_create(state->impl);
45      state->def_set = ralloc_array(NULL, BITSET_WORD, num_words);
46   }
47
48   /* We're going to build a phi.  That's progress. */
49   state->progress = true;
50
51   /* Set the defs set to empty */
52   memset(state->def_set, 0, num_words * sizeof(*state->def_set));
53
54   return state->phi_builder;
55}
56
57static nir_block *
58get_src_block(nir_src *src)
59{
60   if (src->parent_instr->type == nir_instr_type_phi) {
61      return exec_node_data(nir_phi_src, src, src)->pred;
62   } else {
63      return src->parent_instr->block;
64   }
65}
66
67static bool
68repair_ssa_def(nir_ssa_def *def, void *void_state)
69{
70   struct repair_ssa_state *state = void_state;
71
72   bool is_valid = true;
73   nir_foreach_use(src, def) {
74      if (nir_block_is_unreachable(get_src_block(src)) ||
75          !nir_block_dominates(def->parent_instr->block, get_src_block(src))) {
76         is_valid = false;
77         break;
78      }
79   }
80
81   nir_foreach_if_use(src, def) {
82      nir_block *block_before_if =
83         nir_cf_node_as_block(nir_cf_node_prev(&src->parent_if->cf_node));
84      if (nir_block_is_unreachable(block_before_if) ||
85          !nir_block_dominates(def->parent_instr->block, block_before_if)) {
86         is_valid = false;
87         break;
88      }
89   }
90
91   if (is_valid)
92      return true;
93
94   struct nir_phi_builder *pb = prep_build_phi(state);
95
96   BITSET_SET(state->def_set, def->parent_instr->block->index);
97
98   struct nir_phi_builder_value *val =
99      nir_phi_builder_add_value(pb, def->num_components, def->bit_size,
100                                state->def_set);
101
102   nir_phi_builder_value_set_block_def(val, def->parent_instr->block, def);
103
104   nir_foreach_use_safe(src, def) {
105      nir_block *src_block = get_src_block(src);
106      if (nir_block_is_unreachable(src_block) ||
107          !nir_block_dominates(def->parent_instr->block, src_block)) {
108         nir_ssa_def *block_def =
109            nir_phi_builder_value_get_block_def(val, src_block);
110
111         /* If def was a deref and the use we're looking at is a deref that
112          * isn't a cast, we need to wrap it in a cast so we don't loose any
113          * deref information.
114          */
115         if (def->parent_instr->type == nir_instr_type_deref &&
116             src->parent_instr->type == nir_instr_type_deref &&
117             nir_instr_as_deref(src->parent_instr)->deref_type != nir_deref_type_cast) {
118            nir_deref_instr *cast =
119               nir_deref_instr_create(state->impl->function->shader,
120                                      nir_deref_type_cast);
121
122            nir_deref_instr *deref = nir_instr_as_deref(def->parent_instr);
123            cast->mode = deref->mode;
124            cast->type = deref->type;
125            cast->parent = nir_src_for_ssa(block_def);
126            cast->cast.ptr_stride = nir_deref_instr_ptr_as_array_stride(deref);
127
128            nir_ssa_dest_init(&cast->instr, &cast->dest,
129                              def->num_components, def->bit_size, NULL);
130            nir_instr_insert(nir_before_instr(src->parent_instr),
131                             &cast->instr);
132            block_def = &cast->dest.ssa;
133         }
134
135         nir_instr_rewrite_src(src->parent_instr, src,
136                               nir_src_for_ssa(block_def));
137      }
138   }
139
140   nir_foreach_if_use_safe(src, def) {
141      nir_block *block_before_if =
142         nir_cf_node_as_block(nir_cf_node_prev(&src->parent_if->cf_node));
143      if (nir_block_is_unreachable(block_before_if) ||
144          !nir_block_dominates(def->parent_instr->block, block_before_if)) {
145         nir_if_rewrite_condition(src->parent_if, nir_src_for_ssa(
146            nir_phi_builder_value_get_block_def(val, block_before_if)));
147      }
148   }
149
150   return true;
151}
152
153bool
154nir_repair_ssa_impl(nir_function_impl *impl)
155{
156   struct repair_ssa_state state;
157
158   state.impl = impl;
159   state.phi_builder = NULL;
160   state.progress = false;
161
162   nir_metadata_require(impl, nir_metadata_block_index |
163                              nir_metadata_dominance);
164
165   nir_foreach_block(block, impl) {
166      nir_foreach_instr_safe(instr, block) {
167         nir_foreach_ssa_def(instr, repair_ssa_def, &state);
168      }
169   }
170
171   if (state.progress)
172      nir_metadata_preserve(impl, nir_metadata_block_index |
173                                  nir_metadata_dominance);
174
175   if (state.phi_builder) {
176      nir_phi_builder_finish(state.phi_builder);
177      ralloc_free(state.def_set);
178   }
179
180   return state.progress;
181}
182
183/** This pass can be used to repair SSA form in a shader.
184 *
185 * Sometimes a transformation (such as return lowering) will have to make
186 * changes to a shader which, while still correct, break some of NIR's SSA
187 * invariants.  This pass will insert ssa_undefs and phi nodes as needed to
188 * get the shader back into SSA that the validator will like.
189 */
190bool
191nir_repair_ssa(nir_shader *shader)
192{
193   bool progress = false;
194
195   nir_foreach_function(function, shader) {
196      if (function->impl)
197         progress = nir_repair_ssa_impl(function->impl) || progress;
198   }
199
200   return progress;
201}
202